diff --git a/GPy/util/warping_functions.py b/GPy/util/warping_functions.py
index e05f39af..35ad3b80 100644
--- a/GPy/util/warping_functions.py
+++ b/GPy/util/warping_functions.py
@@ -222,7 +222,7 @@ class TanhWarpingFunction_d(WarpingFunction):
         """
 
 
-        mpsi = psi.coSpy()
+        mpsi = psi.copy()
         d = psi[-1]
         mpsi = mpsi[:self.num_parameters-1].reshape(self.n_terms, 3)